If you weren't doing anything you weren't 'technically' supposed to do with it, such as cutting corners, then the cube certainly shouldn't fall apart. If I install a newly purchased doorknob, for arguments sake, I would definitely expect the doorknob to hold for at least a day or longer. In purchasing this doorknob from the seller, I assume that the seller is selling a FULLY FUNCTIONAL AND QUALITY TESTED item. Therefore, this is obviously a quality problem, not an assembly problem.
Also, the immediate falling apart of your NEWLY PURCHASED cube probably indicates some form of bad quality or broken part. Therefore, you should probably request a replacement or a refund, as a broken cube obviously doesn't meet 'quality requirements.'